I. Field of the Invention
This invention relates generally to power tools used for metal working, and more particularly to a machine for preparing industrial tubing by squaring the end thereof prior to joining same to another tube or fitting in a welding operation and/or for trimming such a tube to a precise length in plumbing a fluid flow system.
II. Discussion of the Prior Art
The E.H. Wachs Company of Welling, Ill., produces and sells a tube squaring tool that conforms to the teachings of the Pierce U.S. Pat. No. 5,619,893. It comprises a hand-held, electrically-powered drive motor similar in construction to a conventional 1/2" power drill with a pistol grip, but instead of supporting a drill bit in a chuck, the motor shaft is coupled to a coaxially aligned shaft of the tube squaring tool which has a cutting tool retainer formed at the free end thereof. Surrounding the squaring tool shaft is a housing that is fixedly clamped to the drive motor housing at one end thereof, with the opposite end including a collet retainer for holding a collet used to clamp a tubular workpiece to be squared. Coaxially disposed about the housing is a feed nut having internal threads that mesh with external threads on a feed ring. When the feed nut is rotated in a clockwise direction, the shaft is displaced axially toward the end of the tube workpiece to be squared. In this manner, the rotatable cutting tool may be brought into contact with the end of a tube to thereby shave material from it.
Unfortunately, tube squaring machines conforming to the Pierce patent have a serious design flaw that adversely impacts the quality of the machining operation being performed. The shaft is journaled for rotation at two relatively closely spaced locations proximate the midpoint of the shaft such that a substantial portion of the tool's shaft and the weight of the tool holder portion thereof is cantilevered relative to the journal bearings. The cantilevered shaft length increases as the feed nut is rotated to advance the cutting tool toward the stationary workpiece. It is found that after a relatively short period of use, the cutting tool not only rotates but wobbles in a plane perpendicular to the normal axis of the shaft resulting in "chattering". This chattering leads to irregularities in the end of the tube being machined. In addition, the bearings themselves are subject to relatively rapid wear that requires that the tool be taken out of service for refurbishment.